Grain-oriented electrical steel sheet and manufacturing method thereof

1. A grain-oriented electrical steel sheet having a composition comprising 0.8 mass % to 7 mass % of Si, 0.05 mass % to 1 mass % of Mn, 0.0005 mass % to 0.0080 mass % of B, 0.005 mass % or less of each of Al, C, N, S and Se, and a balance comprising Fe and inevitable impurities, and having a glass coating film, comprising a composite oxide mainly comprising forsterite on a steel sheet surface, wherein:

a peak position of B in emission intensity from the steel sheet surface is different from and deeper than a peak position of Mg in emission intensity when glow discharge optical emission spectrometry (GDS) is performed, and

out of peaks of B in emission intensity observed by the glow discharge optical emission spectrometry (GDS), a peak occurrence time tB of a peak that is the farthest from the steel sheet surface is expressed by the following Expression (1):

tMg×1.6≤tB≤tMg×5  (1)

where tMg represents a peak occurrence time of Mg, and the peak position of B, Mg, the values tB and tMg are measured by the GDS on a surface of a secondary coating film containing 26 to 38 mass % of colloidal silica, 4 to 12 mass % of one type or two types selected from the group consisting of chromium anhydride and chromate, and a balance comprising aluminum biphosphate, and having a thickness of not less than 1 μm nor more than 2 μm.

2. A manufacturing method of the grain-oriented electrical steel sheet according to claim 1 , comprising:

at a predetermined temperature, heating an electrical steel sheet material containing Si of 0.8 mass % to 7 mass %, acid-soluble Al of 0.01 mass % to 0.065 mass %, N of 0.004 mass % to 0.012 mass %, Mn of 0.05 mass % to 1 mass %, B of 0.0005 mass % to 0.0080 mass %, at least one type selected from a group consisting of S and Se of 0.003 mass % to 0.015 mass % in total amount, a C content of 0.085 mass % or less, and a balance being composed of Fe and inevitable impurities;

performing hot rolling of the heated silicon steel material to obtain a hot-rolled steel strip;

performing annealing of the hot-rolled steel strip to obtain an annealed steel strip;

performing cold rolling of the annealed steel strip one time or more to obtain a cold-rolled steel strip;

performing decarburization annealing of the cold-rolled steel strip to obtain a decarburization-annealed steel strip in which primary recrystallization has been caused;

applying an annealing separating agent having MgO as its main component on the decarburization-annealed steel strip;

finish annealing the decarburization-annealed steel strip and thereby causing secondary recrystallization;

and further performing a nitriding treatment in which an N content in the decarburization-annealed steel strip is increased between start of the decarburization annealing and occurrence of the secondary recrystallization in the finish annealing, wherein

the predetermined temperature, when S and Se are contained in the silicon steel material, is a temperature T1 (° C.) expressed by Expression (2) below or lower, a temperature T2 (° C.) expressed by Expression (3) below or lower, and a temperature T3 (° C.) expressed by Expression (4) below or lower,

when no Se is contained in the silicon steel material, the predetermined temperature is the temperature T1 (° C.) expressed by Expression (2) below or lower and the temperature T3 (° C.) expressed by Expression (4) below or lower,

when no S is contained in the silicon steel material, the predetermined temperature is the temperature T2 (° C.) expressed by Expression (3) below or lower and the temperature T3 (° C.) expressed by Expression (4) below or lower, and a finishing temperature Tf of finish rolling in the hot rolling satisfies Expression (5) below,

amounts of BN, MnS, and MnSe in the hot-rolled steel strip satisfy Expressions (6), (7), and (8) below, and at the time of finish annealing, a temperature falls within a temperature range of 800° C. to 1100° C. and an atmosphere satisfies Expressions (9) and (10) below,

T1=14855/(6.82−log([Mn]×[S]))−273  (2)

T2=10733/(4.08−log([Mn]×[Se]))−273  (3)

T3=16000/(5.92−log([B]×[N]))−273  (4)

Tf≤1000−10000×[B]  (5)

B asBN ≥0.0005  (6)

[B]−B asBN ≤0.001  (7)

S asMnS +0.5×Se asMnSe ≥0.002  (8)

0.75≥P N2 ≥0.2  (9)

−0.7>Log [P H20 /P H2 ]  (10)

here, [Mn] represents the Mn content (mass %) of the silicon steel material, [S] represents the S content (mass %) of the silicon steel material, [Se] represents the Se content (mass %) of the silicon steel material, [B] represents the B content (mass %) of the silicon steel material, [N] represents the N content (mass %) of the silicon steel material, B asBN represents an amount of B (mass %) that has precipitated as BN in the hot-rolled steel strip, S asMns represents an amount of S (mass %) that has precipitated as MnS in the hot-rolled steel strip, and Se asMnSe represents an amount of Se (mass %) that has precipitated as MnSe in the hot-rolled steel strip; further, P N2 represents a nitrogen partial pressure, and P H2O and P H2 represent a water vapor partial pressure and a hydrogen partial pressure respectively.

3. The manufacturing method of the grain-oriented electrical steel sheet according to claim 2 , wherein

at the time of finish annealing, the temperature falls within the temperature range of 800° C. to 1100° C. and the atmosphere satisfies Expression (11) below,

4 Log [P N2 ]=3 Log [P H2O /P H2 ]+A+3455/T  (11)

here, −3.72≥3 Log [P H2O /P H2 ]+A≥−5.32 and −0.7≥Log [P H2O /P H2 ] are satisfied and A represents a constant determined in such a manner that 3 Log [P H2O /P H2 ]+A falls within a predetermined range according to Log [P H2O /P H2 ], and T represents the absolute temperature.

4. The manufacturing method of the grain-oriented electrical steel sheet according to claim 2 , wherein

at the time of finish annealing, an atmosphere at 1100° C. or higher satisfies Expressions (12) and (13) below,

0.1≥P N2   (12)

−2≥Log [P H2O /P H2 ]  (13).

5. The manufacturing method of the grain-oriented electrical steel sheet according to claim 2 , wherein

the electrical steel sheet material further contains at least one type selected from a group consisting of Cr: 0.3 mass % or less, Cu: 0.4 mass % or less, Ni: 1 mass % or less, P: 0.5 mass % or less, Mo: 0.1 mass % or less, Sn: 0.3 mass % or less, Sb: 0.3 mass % or less, and Bi: 0.01 mass % or less.